Flow sensors are utilized in a variety of fluid-sensing applications for detecting the movement of fluids, which may be in gaseous (e.g., air) or liquid form. A gas mass flow sensor is one example of a flow sensor. Examples of gas sensing applications utilizing mass gas flow sensors include anesthesia gas mixers employed in medical applications, high-end welding equipment utilized in industrial applications, and gas chromatography detectors and controllers implemented in instrumentation applications. Typical sensor instrumentation utilized in such applications includes, for example, one or more simultaneous measurand to make calculations for sensor measurement. This is currently achieved by either using multiple sensors with different addresses or a single sensor with a complex system level calibration selection that utilizes a conditioning microcontroller or a PLC (Programmable Logic Controller).
Flow sensors inherently produce a nonlinear output signal in response to gaseous or liquid flow through the sensor. Such nonlinear output signals are dependent upon many factors, such as temperature coefficients of resistance with respect to the utilized sensing element, thermal transfer characteristics of the media being measured and the media of the transducer, and the mechanical dimensions of a flow path.
Signal conditioning circuits are often utilized as an interface in a signal conditioning unit to convert a basic flow signal received from a data source into a more usable output signal. Signal conditioning circuits can be utilized in association with flow sensors to receive a non-linear flow signal and convert the basic flow signal into an output voltage utilized by a control system. Application Specific Integrated Circuit (ASIC) components have been developed for conditioning sensor input signals and such ASIC's offer a wide variety of programming options that can be specifically tailored to match the characteristics of the particular sensor technology.
The majority of prior art sensing applications possess limited sensing and signal conditioning capabilities. Such sensing applications utilize multiple sensors, complex calibration routines and expensive micro-controllers/PLCs to condition basic flow signals from the sensor, regardless of the quantity being measured by the sensor. This approach results in a complex system calibration, which leads to an increase in processing time and often produces inaccurate results. Additionally, the installation costs for packaging individual sensors for such application increases, which further enlarges the size of the final sensor package.
Based on the foregoing it is believed that a need exists for an improved multi-gas flow sensor utilizing a combi sensor with gas calibration capability as described in greater detail herein. A need also exists for an improved signal conditioning circuit that is capable of conditioning the basic flow signal output from different types of sensors.